1. Field of the Invention
The present invention relates generally to Multi Input Multi Output (MIMO) systems, and more particularly, to an apparatus and method for spatial multiplexing capable of supporting a large number of data streams in a MIMO system.
2. Description of the Related Art
A great deal of research has been conducted in the area of system capacity in MIMO communication systems.
In association with the MIMO communication systems, an Orthogonalized Spatial Multiplexing (OSM) method has been proposed whereby a simple receiver is allowed to perform simple Maximum Likelihood (ML) decoding using a small amount of feedback information. In the OSM method, channel orthogonality can be determined when a transmitter performs a simple conversion operation.
The OSM method is a transmission method for a closed-loop MIMO communication system. Unlike an open-loop system, the closed-loop system performs precoding before symbols are transmitted by a transmitting end, and receives information for the precoding from a receiving end through a feedback channel path.
The OSM method can utilize single phase information θ as feedback channel information. Through the use of the single phase information θ, the transmitting end can rotate a Transmit (Tx) symbol vector by performing preceding, and thus can perform a desired transmission. Further, the OSM method provides excellent transmission performance in the closed-loop MIMO system having only a single feedback phase information and low Receive (Rx) complexity.
However, in the OSM method only two Tx symbols (i.e., two data streams) can be transmitted due to a structural feature of precoding. A system having two or more Tx antennas can maximize performance in combination with an antenna selection method. However, in this case, a data rate decreases since a multiplexing gain cannot be maximized.